How do you apply aikido principles of non-violence and harmony in a combat situation as a soldier?

It is challenging for sure, however, I don't think impossible.

I think we have to think in a much bigger perspective than the immediate threat we face.

Aikido at it's best in harmony and balance. Harmony and balance come from the alignment and attunement of mind, body, and spirit.

I will have to go back and dust off my Mushashi a little bit, but I think he hit it on the head. A warrior must be complete. He must make the appropriate decisions at the right time with all the input and information that he has.

How clear that information is to the warrior depends on perspective. You have to prepare yourself and lead a balanced life. Train hard, and make sure you are well prepared, mentally, spiritually, and physically.

If you are distracted, mentally, physically, and spiritually tired you cannot make clear decisions.

If you did not take care or your relationship with your spouse back home properly, then when you are downrange things will be worse. You may be worrying about this as you proceed down the road on your patrol, you may miss that vital piece of information that is between life and death.

Budo is not always about facing direct violence and being able to resolve that issue, but a much bigger once that is much more influencial and long lasting.

I think that there were many, many things that les to the actual engagement of violence that occurred, how can we expect to peacefully resolve it in a matter of seconds or minutes all the time?

I think Budo prepares us in a much greater way for peace and harmony than all the small battles and struggles we face.

I think there is much in Mushasi's writings to ponder concerning this.